Fabrication of RE-doped GaN ELDs


Fabrication of DC ELDs (Don)

DC ELDs consist of ITO Schottky electrodes fabricated on rare-earth-doped GaN (GaN:RE) thin films grown on Si or sapphire substrates. For the fabrication, an ITO film (90% In2O3 and 10% SnO2) is rf sputtered onto the GaN:RE films to make optically transparent film contacts. Liftoff or etching procedures are used in ELD patterning. The ITO film was sputtered under ~ 150 W, 5 mTorr Ar plasma with a plasma induced DC bias of ~ 300 V. After the sputter deposition and a following annealing at 400 - 450 C in an N2 ambient, the main ITO film characteristics were: 400 ~500 nm thickness, ~10 W /square sheet resistance and greater than 85% transmission over the visible spectrum. A typical ring-shaped electrode has an area of 7.65 10-4 cm2 and its detailed structure is shown in the following figure. Either top or bottom contact can be used for a ground electrode.
















Fabrication of AC Devices (Bob J.)

Black thick dielectric ac electroluminescence devices (BDEL) utilizing GaN doped with rare earths (Er-green, Eu-red, Tm-blue) have been developed at the University of Cincinnati Nano-Electronics Laboratory for flat panel device applications. The BDEL device structure operates by applying an ac voltage that is capacitivly coupled to a phosphor which emits light during reversible electrical breakdown. The rare earths are excited by hot electron impact excitation during GaN:RE phosphor break down.  Thus, the sharp line admissions of the rare earths doped into the wide band gap GaN host (3.4 eV) form an ideal durable material for flat panel display applications.  In the BDEL fabrication process: (1) patterned Indium Tin Oxide (ITO) column electrodes are sputtered onto the viewing glass, (2) a thin dielectric is sputtered, (3) the GaN:RE phosphor is deposited by Molecular Beam Deposition (MBD), (4) a thin dielectric is sputtered, the thick black dielectric is printed, and (5) patterned Al row electrodes are sputtered.  The MBD system, from SVT Associates, is similar to MBE except with base pressures at 10-9 and the absence of a substrate lattice necessary for epitaxial growth.    Unlike Shotcky diode electroluminescence devices (dc-ELD), traditional thin film electroluminescence devices (TFEL), and Organic Light Emitting Displays (OLED), the thick film provides protection against shorts caused by small fabrication defects (fig 2).  This enables fabrication with less costly facilities and greater dependability. Unlike the inverted thick dielectric electroluminescence devices (iTDEL) the BDEL devices are fabricated using the viewing glass as the substrate.  This avoids the high cost associated with ceramic substrates and eliminates the need for additional planarization fabrication steps necessary to smooth the rough ceramic surface. In less than two years of development this technology has experienced growth from fabrication of simple 3 mm test device dots to a 40 x 30 matrix addressed monochrome display utilizing GaN:Eu as the active phosphor.  This technology is presently being developed with collaboration from Extreme Photonix LLC.  Further information can be obtained from previous publications in IEEE and the SID digest.